The present invention pertains to location determination services and more particularly to location determination for mobile units.
Historically, location determination has been performed by complex radio frequency computing equipment. One example of the use of location services is for the location of troops and vehicles within a bounded, simulated battlefield. Munitions or small arms fire would be simulated or introduced into the battlefield setting. The position of the munitions is known. The position of various soldiers and vehicles within the battlefield is determined and the effects of the munitions upon the soldiers and vehicles is determined. One such system is shown in U.S. Pat. No. 4,976,619, issued to the same assignee as the present application.
More modern location determination equipment typically employs the global positioning system (GPS). Range measurements are taken from a number of geosynchronous satellites and processed in order to determine the location of a mobile unit and accompanying user virtually anywhere on earth. Global positioning system locations are typically very accurate. Differential GPS location may be performed to obtain even greater accuracy. Global positioning service location receivers typically do not work well if at all within large buildings or underground. Any area which includes substantial electromagnetic shielding will attenuate the GPS signals to make them unusable by a receiver. Also, from time to time the GPs system may be unavailable.
Accordingly, what is needed is a method for determining location of a mobile unit inside buildings, shopping malls or underground, etc.